1. Technical Field
Various embodiments of the present disclosure relate to electronic circuits including bipolar junction transistors.
2. Related Art
A power supply voltage applied to an integrated circuit may vary due to various factors. The variation of the power supply voltage may affect operation currents of the integrated circuit and may even cause malfunctions of the integrated circuits. Thus, it is important to design a reference voltage generator or a reference current generator that produces a constant voltage level or a constant amount of current regardless of the variation of the power supply voltage. It is also important to minimize temperature sensitivity of the reference voltage generator or the reference current generator.
A reference voltage may be obtained by generating a constant voltage based on a band gap voltage of a silicon material. In general, a reference voltage circuit may include a pair of bipolar junction transistors, which have different current densities, and are coupled in parallel. In such a case, while an emitter-base voltage of each of the bipolar junction transistors has a positive temperature coefficient, a voltage difference between the emitter-base voltages of the pair of bipolar junction transistors may have a negative temperature coefficient. If the positive temperature coefficient and the negative temperature coefficient may be appropriately controlled to have the same absolute value, the reference voltage circuit may generate a constant reference voltage regardless of temperature variation. This reference voltage is known as close to the band gap voltage of the silicon material at zero (0) degree of the absolute temperature (OK). Also, this reference voltage circuit is referred to as a band gap reference (BGR) circuit. The BGR circuit is known as stable to the temperature variation, and widely used in integrated circuits. That is, if collector resistance values of the bipolar junction transistors may be appropriately controlled to cancel the positive temperature coefficient and the negative temperature coefficient of the bipolar junction transistors, the BGR circuit may generate a stable and constant reference voltage regardless of temperature variation. However, if the bipolar junction transistors are employed in the BGR circuit, the integration density of the BGR circuit may be degraded.